Accumulator



Patented Apr. 7, 1942 'UNITED STATES- PATENT OFFICE ACCUMULATOR Harold Caminez, Hackensack, N. J.,'asslgnor to Air Associates Incorporated, Bendix, N. J., a corporation of New York `Application July 9, 1941, Serial No. 401,622 e claims. icl. 13s-so) This invention relates to an accumulator for a hydraulic system, and more particularly for a hydraulic system for aircraft. Accumulators for the indicated purpose are required to withstand high pressure and at the same time to give the desired performance with maximum safety and minimum weight. Conventional accumulators of a certain type consist of a container divided by an elastic partition or diaphragm into two charnbers one of which is intended to receive air under a preload pressure, the other one to receive, store or deliver hydraulic iiuid according to the instantaneous iluid pressure prevailing in the hydraulic system. The performance of the Vaccumulator essentially depends on the ratio of the preload air pressure to the maximum line pressure of the system, the volume of the chamber containing hydraulic uid at maximum pressure of the system and on the minimum pressure at which the hydraulic system is operative. Under consideration of the relationship it has been found that in hydraulic systems for aircraft operating with a maximum line pressure of about 1500 psi it is advisable to select a preload pressure between 500 and 750 psi, i. e.. between one third and one half the maximum operating pressure of the system. Considering further that with the iilling of the air chamber at half the maximum system pressure only half the actual accumulator volume is available for the storing ci the hydraulic fluid it will be easily understood that an accumulator of relatively appreciable size is required in order to store a reasonable amount of energy in View of the extensive need for hydraulic uid in modern aircraft. Such required size of the accumlator makes it difficult to combine in its construction the above-mentioned features as to low weight, maximum safety and resistance to high pressure, particularly as the construction must also be such that the accumulator when hit by gun ilre will not shatter owing to the rapid expansion of the relatively large volume of compressed air. This requirement of gun re test eliminates certain light weight designs which otherwise might be developed. y

The invention, therefore, contemplates the provision of an accumulator which complies with the mentioned requirements and which may be readily manufactured without prohibitive costs and excessive labor.

The accumulator according to the invention comprises a container of substantially cylindrical shape with end pieces or heads each of which is provided with an a air and of the hydraulic iiuid respectively, and a substantially bag-shaped diaphragm. the interior of which communicates with said aperture for the air.

The invention also consists in a method of making a light container resistant to high internal pressure.

The invention further consists in means for' preventing the bag from forming pockets in the container chamber for the hydraulic iiuid, whereby a quantity of such fluid might be trapped, and also in means to prevent the bag from wrinkllng which might cause'breaks or ruptures in the material.

Further objects and details of the invention will be apparent from the description given hereinafter of embodiments illustrated in the accompanying drawing by way of example. In the drawing:

Fig. l is a longitudinal section of an accumulator according to the invention.

Fig. 2 is a front elevation of a part thereof.

Fig. 3 is a section of the part of Fig. 2 along line 3 3.

Fig. 'i is a longitudinal section of a portion of a modied accumulator.

Referring now to the drawing, the accumulator comprises a container i mainly consisting of a tubular body, cylinder or barrel 2 and two end pieces or heads 3 and li secured thereto by any suitable means. In order to provide for the required strength and light weight the tubular body is preferably made of high strength alloy steel and the heads are substantially cup shaped of high strength aluminum or aluminum alloy forgings screwed and shrunk on the steel cylinder. A leak-proof joint between the parts may be obtained by providing the tubular body 2 close to its ends with external threads 5 and leaving the extreme ends l' and 3 cylindrical. The forgings t and t may have portions 9 and lil respectively which are provided with correspending internal threadings and cylindrical inner faces. In making the connection of the barrel 2 and the heads 3 and d the latter are heated and screwed on the barrel. The dimensions are preferably so selected that the threading takes up the occurring axial forces, whereas the shrink flt ai; the cylindrical portions 'l and 8 ensures the required leak-proof quality, and that at the shrink nt most of the snraintviu be on the steel part withstanding this strain owing to its natural resilience. The heads 3 and 4 have reduced hollow ends Il and l2 to provide ports perture for the entrance of for the admission of air and the hydraulic liquid respectively. Whereas in certain systems it is unnecessary to separate. the air from the hydraulic liquid, the use of oil makes it imperative that a partition be provided which will prevent the formation of a mixture of oil gases with the air. Such mixture might become dangerous owing to its explosiveness since rapid compression of the mixture will. cause a very appreciable rise in temperature. The material of such partition must be elastic in order to alter its shape without wrinkling according to the variations in the volumes of the air and oil chambers formed by such partition. It must be impermeable to either medium and it must not be chemically affected by the oil used as the hydraulic liquid of the system. Materials generally denoted as synthetic rubber are on the market which have the required properties. In the embodiment n'of Fig. 1 the partition or Vdiaphragm is shown as aV substantially cylindrical bag I3 having a restricted neck I4 with opening I4 and a bottom I5 with a hole i5. In order to secure the bag I3 to the container I, the end portion il of the head 3 is provided with an internal ange I6 and threading Il, and the neck I4 of the bag I3 is provided with an external ange I8 bearing against flange I6 when the bag is in assembled position as shown in Fig. l. A nutl I9 is screwed into the threading I'l and compresses flange I8 between flange I6 and a nut shoulder 28. An extension 2! of the nut engaging in the opening I4 of bag I3 has a tubular portion 22 and an interior threading 23. An air valve 24 of any conventional or suitable type is screwed into the threading 23, and a tube 25 is fitted with one of its ends into the tubular portion 22 of the nut I9. Tube 25 is provided with a number of holes 26 and fitted with its other end into a tubularv portion 2l of a retainer 28. This retainer is formed as a plug for the opening I5 of bag I3 and projects with a threaded portion 29 towards the opening of the portion I2 of head 4. Tube 25 serves as a spacer between the neck and bottom of the bag and holds the latter in a coaxial position in relation to container I. A washer 38 and a nut 3| engaging the threading of 29 are provided so as to firmly clamp the bottom I5 of bag I3 between the washer land a shoulder 32 of the retainerv 28. The nut 3I may be secured in its position by means such as the pin 33. The described arrangement of bag I3 with accessorial parts is such that; air blown through valve 24 will enter the tube 25 and pass freely through apertures 26 into the interior of the bag I3 thereby expanding the latter depending on the pressure applied. In order to admit hydraulic fluid into the space between the outside of the bag and the inner surface of the container I, the reduced end I2 of head 4 is interiorly threaded at 34 for connection to the pipe line (not shown) of the hydraulic system and a space 35 is left for the entering fluid between head 4 and the retainer 28. There is also a cup-shaped member 36 arranged inside the head 4 for reasons to be explained hereinafter. This member illustrated more in detail in Figs. 2 and 3 and preferably consisting of sheet metal has a central opening 31 of sufficient size to permit the free end of retainer 28 with nut 3I to pass therethrough, and a maximum diameter d slightly smaller than the inner diameter of the cylinder 2. Cap 36 is further provided with a number of radial grooves 38 so that, channels or conduits are formed from space 35 through grooves 38 and the gap 39 between the periphery of member 36 and barrel 2 to the space between the barrel and bag I3. Finally, it is to be noticed that for reasons to be also explained hereinafter, the wall of bag I3 is shown to gradually decrease in thickness from the bottom I5 to the neck I4. The accumulator may be assembled in the following manner. First, one of the. heads 3 and 4 is screwed and shrunk on the barrel 2 and after the member 36 is placed inside the barrel the other head is screwed and shrunk on the latter; second, tube 25 is inserted into the retainer 28 and nut I9 and passed with the retainer 28 through the wider opening I4 of the bag I3 until the retainer projects from the other opening I5 and the bag flange I8 is in engagement with the shoulder 25 of nut I9. -Then, washer 3D and nut 3l are assembled on the retainer 28 and secured by pin 33. Thereafter. the bag with the retainer 28, spacer tube 25 and nut I9 are inserted into the container from the side of the head 3 and nut I9 is tightly screwed into the threading Il, whereby the bag flange I8 will be clamped in between ange i6 and shoulder 28 and retainer 28 with nut 3| will engage the hole 31 of member 38. It will be clear from the drawing that the so-secured flange I8 serves as a means for holding the bag in position as well as for making the connection leak proof in the manner of a gasket. When valve 24 is screwed into the thread 23 the complete assembly may be connected to a hydraulic system with the aid of the threading 34 of the head 4. Before being provided with the tube 25 and accessorial parts, it is preferable that the bag I3 be about the same shape as shown in Fig. 1. It may be slightly smaller so that it will be slightly stretched by the spacer tube 25. In normal operation the bagwill be lled with air of a predetermined preload pressure through the air valve 24, while there is no pressure of the hydraulic system acting on the outside of the wall of the bag. This preload pressure will expand the bag so that its wall contacts the inner surface of the container I throughout rexcept for the head 4 where the bag will engage the inner surface of the retainer member 38. Hence, the quantity of air charged into the bag through valve 24 is defined by the effective container volume and the preload pressure. This quantity of air remains entrapped in the bag. Although it has been stated that the preload pressure for a system operating with about 1500 psi maximum pressure will preferably be between 500 and 750 psi, this preload pressure should not be smaller than the minimum pressure at which the motors of the system are operative because otherwise a certain quantity of hydraulic liquid would permanently remain in the accumulator for no useful purpose. thus increasing the dead weight of the system. If, now, the hydraulic fluid is admitted lthrough the opening in the end portion I2 of head 4, the uid will enter the space 35 and pass through the channels formed by the grooves 38 and gap 39 so as to flow around the bag compressing the latter and the air therein according. to the pressure instantaneously prevailing in the line system. When maximum system pressure is reached the vair will be compressed to its minimum volume, according to which the volume of the non-innated bag should be originally selected. If, for instance, thek maximum system pressure is 1500 psi and the preload pressure is 1500/2:'750 psi then the volume of the non-inflated bag should be approximately half the volume of the container I because under the indicated conditions the air entrapped in the bag would be compressed to half its original volume which was equal to the container volume. For other ratios of maximum system pressure to preload pressure, the desired volume of the bag can be easily determined by calculation. If in the above example maximum pressure prevails in the system half of the container volume will be illled with the hydraulic fluid under 1500 psi whereby the maximum of energy which can be stored in the accumulator at the selected preload pressure is determined. When the system pressure decreases, expansion of the air will force the fluid back into the system until, at a system pressure equal to the preload pressure, all the uid is expelled from the accumulator except for the dead spaces of the latter.

It will be noticed that the entrapped air under pressure tends to enlarge the bag not only in a radial direction but also axially so as to force the bag into the interior of the entrance port or space 35 of the hydraulic fluid. In order to prevent this and an ensuing dangerous squeezing and wrinkling of the bag, the size of Washer 30 is so dimensioned that its diameter is larger than that of the space 35. In this manner the washer constitutes a shield preventing the bag material from being forced into the port for the fluid. Furthermore, it has been found that a. bag having a wall of equal thickness throughout its length will not always radially expand at the same rate for each portion. Consequently, it might happen that the bag will become deformed as shown in dotted lines at Ml with the result that hydraulic fluid remains enclosed in the cony tainer space near head 3 if the system pressure decreases. In order to prevent such undesirable occurrence, the substantially cylindrical portion of the bag i3 has a wall thickness decreasing from a to b whereby it is ensured owing to the elastic forces of the bag material that the bag will gradually expand from b to a and, upon a decreasing hydraulic pressure, will gradually contract from a to b. Consequently the fluid enclosed in the container will always be assembled near the head i. e. near its port without any danger of being cut off therefrom. For

a similar reason, the retainer 3G is provided, Whose grooves 38 constitute permanently open passages for the fluid even if the bottom of bag ld lies against the wall of the retainer.

it will be noticed that the accumulator according to the invention permits practically the entire quantity of hydraulic fluid stored therein to be utilized in the system. In other words, there are no material dead spaces filled with iluid when the air pressure exceeds the instantaneous'system pressure. Hence, the accumuiator can be built with the minimum capacity required, i. e. without any superfluous weight which would'be objectionable in a system destined for use in aircraft. Furthermore, the accumulator comprises means for holding the diaphragm or bag in its desired axial position relatively to the container whereby wrinkling is avoided which might cause breaks or ruptures particularly if the material of the bag loses its original elasticity at low temperatures as are frequently encountered by aircraft. Similarly, means are provided whereby the bag is prevented from being squeezed into the fluid port owing to the interior air pressure when all fluid is expelled from the container. Other means serve to hold channels permanently open to conduct entering fluid about the gas bag, the latter being sc formed that expansion will gradually take place from the end opposite the uid port whereby` fluid traps are avoided. Finally, the opening in the container head through which the bag is inserted is smaller in diameter than the cylinder, therefore the forces required to safely secure the bag to the cylinder head are considerably less than if a large bag opening were employed. This feature is also helpful in reducing the weight of the accumulator and facilitating the production of a leak proof joint.

The modification illustrated in Fig. 4 relates to the means for preventing the bag from being squeezed into the uid port at the end portion l2 of the container head 4 and from sealing that port. The bag ||3 shown in an inflated state in Fig. 4 differs from the bag I3 of Fig. l only insofar as its bottom H44 is appreciably thicker than the cylindrical portion. On account of internal air pressure, therefore, it will become deformed so as to leave a free space |34 between its outer bottom surface H5 and the inner surface of the head t. 'I'he retainer 28 is passed through the bag as in Fig. 1 and holds the spacer tube 25 slideably inserted therein with its portion 21. A nut |3| with washer |30 clamps the bag against the shoulder 32 of the retainer. Nut |3| isprovided with a iiange |32 which has one or a plurality of holes |33 and which may abut against an interior shoulder I|2 of the head d. Now, it will be clear that bag |I3 will take the position ||5 and that the flange |32 will engage shoulder ||2 when there is an internal superpressure in the air bag II3. If, now, the system pressure rises so as to overcome the air pressure, fluid entering the space 35 will pass through the hole |33 into the space |34 and gradually compress the air bag. Simultaneously the external pressure may force the retainer 28 back on tube 25 a distance equal to the spacing of the end of tube 25 from the bottom |28 of the retainer 28 whereby a gap will occur between should ||2 and nut ange |32 to offer a wider passage to the fluid from space 35 to |34, and the bag takes its original position and shape indicated by the dash lines H3'.

Many modifications and alterations of the i1- lustrated embodiment may be made without departing from the essence of my invention, the scope of which, therefore, shall be limited only by the appended claims.

I claim:

l. An accumulator for a hydraulic system comprising a substantially cylindrical container having reduced ends, each with an aperture, a flexible bag of elastic material coaxially arranged within said container and including a neck and a bottom, a tubular perforated spacer within said bag, means to secure one end of said spacer and the neck of said bag to one of the apertured ends of said container, means in communication with the interior of said spacer and accessible from the outside for admitting compressed air, means to secure the bottom of said bag to the other end of said spacer in position near the other container end, and a shield-like member in connection with the last-mentioned means for preventing expansion of the central bottom portion of said bag in axial direction owing to the internal pressure of said bag.

2. An accumulator for a hydraulic system comprising a substantially cylindrical container having reduced ends, each with an aperture therein,

a flexible bag of elastic material within saidV container, said bag being substantially cylindrical and including a neck and a bottom with a central opening therein, a perforated tubular surfacev of said other container end, said shield y havingaperturesrrto permit uid entering through spacer within said bag, one endof said spacer v and said neck'of said bag being secured to one end of the container in registry with its aperture, means passing through the opening of said bag bottom to attach said spacer thereto, said means including means to seal said bottom opening and to constitute a shield for preventing expansion of the central bottom portion of said bag in axial direction owing to the internal pressure of said bag.

3. An accumulator for a hydraulic system comprising a substantially cylindrical container having reduced ends, each with a central aperture, a flexible bag of elastic material coaxially arranged withn said container and including a neck and a bottom, a tubular perforated spacer within said bag, means to secure said neck of said bag and one end of said spacer toy one of the containerends in registry with its aperture,

means to secure the other end of the spacer to the bottom of said bag in position near the aperture of the other container end, and means for holding at least the central portion of said bottom at a predetermined distance from the aperture and the inner surface of the other container end, said last-mentioned means including a con- 1 duit to permit fluid entering through the aperture of said other container end to pass between the latter and the bottom of the bag.

4. An accumulator for a hydraulic system comprising a substantially cylindrical container having reduced ends, each With a central aperture, a exible bag of elastic material coaxially arranged within said container and including a neck anda bottom, a tubular perforated spacer within said bag, means to secure said neck of said bag and one end of said spacer to one of the container ends in registry with its aperture, a member secured to the bottom Wall of said bag and axially shiftable on the other end of said spacer, and a shield secured to said member the aperture of said`otherV container end to pass between the latter and the bottom of the bag.

5. An accumulator for a hydraulic system comprising a substantially,cylindrical container'hav- Y ing substantially cup-shaped ends, each with a central aperture, a ilexible bag of elastic material coaxially arranged within said container and including a neck and a bottom, a tubular perforated spacer Within said bag, means to secure said neck of said bag and one end of said spacer to one of the container ends in registry with its aperture, means to secure the other end of the spacer to the bottom of said bag in position near the aperture of the other container end, and a member having a radially grooved outer surface substantially shaped in correspondence to the inner surface of said other container end but with a diameter slightly smaller than the inner diameter of the cylindrical portion of said container, said member being arranged between the latter and said bag. A.

6. An accumulator f or a hydraulic system comprising a container including a cylindrical barrel and cup-shaped end pieces screw-and-shrunkconnected to said barrel, each of said end pieces having a central aperture one of which is larger than the other, a flexible bag of elastic material including a neck and a bottom, saidbag ,being arranged interiorly of and coaxially within said container, a tubular perforated spacer within said bag, the neck of said bag with one of the ends of the spacer therein being secured to the container in registry with said larger aperture, the other end of said spacer being secured to the bottom of said bag near the aperture of the other container end, and means between said bottom of said bag and said other container end for 'preventing said bottom from squeezing into the aperture of said other end, and for conducting fluid from the aperture of the lattertowards the inner surface of said barrel when the bag is expanded owing to internal pressure.

. A HAROLD CAMINEZ. 

